The present invention relates to sewage treatment and, more specifically, to treatment apparatus suitable for installation and use with single or small multi-unit dwellings for converting raw sewage to harmless effluent.
The sewage treatment system disclosed in U.S. Pat. No. 3,677,409 includes a tank divided into aeration and settling compartments with means for returning sludge from the latter to the former. Also, a filtering screen with continuous backwash means to prevent clogging is provided, together with skimmer means for removing foam and flowing solid materials from the settling compartment and returning them to the aeration compartment. The tank is molded Fiberglas, bulbous in shape, of circular cross section as viewed from above.
Although the sewage treatment apparatus described above provides a number of desirable features, there are still some areas of objection. For example, the cost of molds for the plastic tanks makes the unit cost very high in limited quantities. Also, the shape of the tank requires deep excavation in relation to tank volume for underground installation, which is also very expensive or unfeasible in some locations. Finally, while the effluent is relative pure and free of pollutants, it requires discharge into a sand filter bed, or the like, being unsafe for discharge into a natural waterway.
Accordingly, it is a principal object of the present invention to provide a sewage treatment system of high efficiency, i.e., which converts raw sewage to extremely pure effluent.
A further object is to provide a high efficiency sewage treatment system which is economical in manufacture and below-ground installation relative to its capacity.
Another object is to provide a sewage treatment system having improved means for filtering solids to produce a purified effluent.
Other objects will in part be obvious and will in part appear hereinafter.